This invention relates to a lubricant for metal forming, which can form a lubricating film on a metal surface by virture of the heat generated by deformation or friction during the metal forming such as cold forming i.e. forming without heating of a metallic workpiece, etc., and also to a process for metal forming with said lubricant.
A lubricant for metal forming must have a satisfactory lubricating ability up to an elevated temperature caused by deformation, friction, etc. and also to increasing new surface area of a workpiece created by the metal formation. The lubricants so far proposed for this purpose are water-soluble or water-insoluble liquid lubricants containing mineral oil or synthetic oil or their mixture as the major component and further containing a semi-solid lubricant such as metal soap, beef tallow, etc., a sulfur-based, chlorine-based, or phosphorus-based extreme pressure agent, or a solid lubricant such as graphite, molybdenum disulfide, etc. These lubricants can be used, without any problem, for the metal forming with low reduction of area, but in the case of high reduction of area which produces a higher temperature or a higher surface pressure, or in the case of forming products of complicated shapes, their load-carrying capacity, heat resistance, etc. are not satisfactory, resulting in galling. For the lubrication for larger plastic deformation, or forming products of complicated shapes, it has been so far proposed to plate a workpiece surface with a soft metal, such as copper, zinc, etc., or to coat a workpiece surface with a plastic resin film, or to conduct phosphate coating or oxalate coating of a workpiece surface. These lubricating coating treatments require a sufficient pretreatment and complicated coating steps, and thus require much labor and large costs and also have further problems of removing the coatings after the forming or of environmental pollution by the waste liquor from the coating treatments or removal of the coatings after the forming.
Recently, lubricants containing phosphoric acid or its salts, boric acid or its salts, carbonates, nitrates, sulfates, or hydroxides of alkali metal, and laminar silicate, etc. have been proposed (Japanese Patent Application Kokai (Laid-open) No. 57-73089). However, since they consist of water-soluble glass powder of P.sub.2 O.sub.5, B.sub.2 O.sub.2 and M.sub.2 O (where M represents an alkali metal), and the laminar silicate, or their mixture and water, they fail to show lubrication at a low temperature forming such as cold forming, and thus cannot be used as lubricants for cold forming.
Furthermore, an acidic lubricant for cold forming, which is prepared by reaction of a multivalent metal cation, orthophosphate, and alkyl alcohol or alkylaryl alcohol having 10 to 36 carbon atoms, and which has a water content of not more than 20% by weight has been proposed (Japanese Patent Publication Kokai (Laid-open) No. 47-15569), and lubricants further containing mineral oil, carboxylic acid, and alkylamine besides the said acidic lubricant, for example, lubricants for cold forming, which comprises 30 to 95% by weight of an organic lubricant such as mineral oil, oleic acid, or oleylamine, 5 to 60% by weight of a reaction product of a multivalent metal cation, polyphosphoric acid and an alcohol having 10 to 36 carbon atoms in a ratio of the metal cation:P.sub.2 O.sub.5 :the alcohol=1:3-60:14-150 by weight, and 0.5 to 10% by weight of water have been proposed (U.S. Pat. No. 3,932,287). These lubricants show good results in drawing of pipes, etc., but fail to meet the requirements for forming steel workpieces with high reduction of area.